Question

The coordination number of \(\mathrm{Al}\) in the crystalline state of \(\mathrm{AlCl}_{3}\) is ___.

Short answer

The coordination number of Al in the crystalline state of AlCl3 is 6.

Step-by-step solution

Understand the Concept of Coordination Number

The coordination number of an atom in a crystal is the number of atoms, ions, or molecules that a central atom or ion can surround itself with in a crystal lattice. In ionic compounds, it refers to the number of opposite-charge ions that surround the ion in the crystal lattice.

Determine the Structure of AlCl3

Aluminum chloride (AlCl3) exists in different forms depending on the state (solid or gaseous). In the solid state, AlCl3 has a layer lattice structure where each Al ion is surrounded by six Cl^- ions. This forms an octahedral geometry around the aluminum ion.

Identify the Coordination Number of Al

Since each aluminum ion is surrounded by six chloride ions in the crystalline form of AlCl3, the coordination number of Al in AlCl3 is six.

Key concepts

Crystalline State

Imagine holding a precisely cut diamond in your hand, its sparkling facets each perfectly aligned. This mesmerizing regularity is because the diamond is in a crystalline state, which means it boasts a highly ordered structure at the microscopic level. Similarly, many solids form a definite and repeating pattern, extending in all three dimensions. These patterns are not just mere aesthetic charms. They reveal the solid's intrinsic properties, from melting points to electrical conductivity.
In a crystalline state, the orderly arrangement allows us to predict how atoms or molecules within the solid will interact with one another or with other substances. It helps us understand reactions and identify how materials might perform under different conditions. The predictability of the crystalline state is, thus, of paramount importance for scientists and engineers when designing new materials or studying the properties of existing ones.

Ionic Compounds

The world of salt we sprinkle on our French fries and the chalk we use on blackboards is where the fascinating concept of ionic compounds comes into play. When thinking about ionic compounds, envision a silent dance of positively charged ions called cations and negatively charged ions named anions. This dance occurs because of an elegant exchange of electrons; one atom donates, while the other accepts, resulting in a bond of mutual need — the ionic bond.
What makes ionic compounds particularly interesting is the contrast in properties they exhibit in comparison to covalent compounds. Ionic compounds typically have high melting and boiling points, are solid at room temperature, and conduct electricity when melted or dissolved in water. This is due to the strong electrostatic forces holding the ions in a definitive spatial arrangement. Through understanding ionic compounds, chemists can predict behaviors of substances, from the mundane table salt to the complex workings of batteries.

Crystal Lattice Structure

The elegant geometry that forms the backbone of many substances can be explained by delving into their crystal lattice structure. This is not merely a network of connections but an intricate arrangement of atoms, ions, or molecules in a three-dimensional space — much like the framework of a skyscraper that determines its sturdiness and design. For compounds such as aluminum chloride (AlCl_3), it's the crystal lattice that dictates how each aluminum ion coordinates with its neighboring chloride ions.
Within this structure, we find the essence of material properties. The strength of the ionic bonds within the crystal lattice dictates the hardness of the material, its melting point, and other physical attributes. By studying these lattice structures, we can predict how a substance will interact with its environment, helping us in everything from creating stronger materials for construction to developing new pharmaceuticals.